I have a 1995 Toyota Avalon that has a persistent miss, that according to
the Diagnostic Tool is P3040 (Misfire detected on cyclinder 4), I was
supplied this code from my local Advance Auto Parts Store. After not being
able to figure out, on my own, what was the problem with the cyclinder, I
took it to the Toyota dealership, the mechanic at the dealership seems to
think that the problem may be with the valve seal guides or a stick piston
ring in cyclinder four. The compression check on this cyclinder is much
lower than the other cyclinders. My guess is that the problem is the valve
guide seal, and the reason I think so is because sometimes after letting
the car set for a few hours and when it's started smoke comes from the
exhaust.

Anyone, what's your take on this issue?

"cea1" <cea1 (AT) comcast (DOT) net> wrote

The technician who looked at the car has a big advantage over everyone here
since he or she was able to examine the general condition of the car and
engine.

The tech should have been able to get a general idea about the condition of
the rings by seeing if the compression improves in a wet test.

Leaking valve stem seals will not in itself result in lower compression
although smoke out of the exhaust is a symptom.
--
Ray O
correct the return address punctuation to reply

Hi Ray,

Please explain the wet test.

cea1

"cea1" <cea1 (AT) comcast (DOT) net> wrote

To take cylinder compression readings, the spark plug is removed, a
compression gauge is installed in the spark plug opening, the engine is
cranked, and the peak compression for the cylinder is recorded. This is
known as a "dry" compression reading. After recording the dry compression
reading, the compression gauge is removed and some engine oil is squirted
into the spark plug hole, the compression gauge is re-installed, the engine
is cranked, and the compression reading is recorded again. This is known as
a "wet" reading. If the compression reading increases when oil is squirted
into the cylinder, it indicates that the piston rings may be bad because the
oil acts to seal some of the leakage.

--
Ray O
correct the return address punctuation to reply

I understand it completely now, thank you for the explanation.

cea1

"cea1" <cea1 (AT) comcast (DOT) net> wrote

--
Ray O
correct the return address punctuation to reply

Interesting. Just like Ray pointed out, a worn valve guide seal has no
bearing on compression. The problem may very well be poor sealing at the
rings, but you can't make that determination from a dry compression test.
Like Ray said, you have to do a wet compression test also.
If I had this car in my bay and observed the condition you described, I
would recommend doing a cylinder leak-down test. They are MUCH more
effective in the information they provide compared to a simple compression
test, but also more involved. It involves finding TDC on the tested
cylinder and jamming air at about 90psi in through the spark plug hole. If
there is a compression loss, you will be able to see it on the gauge and
see it leaking from the engine. If there are bubbles pouring out of the
radiator cap, you have a bad head gasket. If there is air coming out of
the exhaust or intake, you have a valve problem, and air in the crankcase
would point to a bad ring or two.
The problem with compression tests is that they only measure a cylinders
sealing relative to the surrounding cylinders. There are a lot of variables
(cam lift, cranking speed, etc) that can affect readings. The leakdown test
is a pinpoint measurement and should be standard procedure before digging
in for a rebuild.

On Wed, 21 Dec 2005 12:53:08 -0600, "Ray O"
<rokigawa (AT) tristarassociatesDOT (DOT) com> wrote:
And if the compression on one cylinder is unusually low but the wet
test does not improve the readings, there is probably a bad valve or a
valve seat problem. Or it's a blown head gasket issue.

To narrow down the problem further, they put another adapter in the
spark plug hole called a "Leakdown Tester" that has an air chuck and a
pressure gauge.

You put the engine at top dead center for that cylinder and hold it
in place, then apply compressed shop air into the cylinder through the
adapter. If you hear hissing from the tailpipe, it's the exhaust
valve, from the intake manifold and it's the intake valve.

If the radiator starts bubbling it's not the valves... Head Gasket.
But this usually reveals itself in overheating issues.

--<< Bruce >>--

--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
5737 Kanan Rd. #359, Agoura CA 91301 (818) 889-9545
Spamtrapped address: Remove the python and the invalid, and use a net.

Bruce,

Thanks for the info. Can I purchase a Leakdown Tester from many parts
store, or is this a tool that's generally only available at an auto repair
shop?

Oh by the way, do you know what DTC code P01300 means?

cea1

Thanks, qslim!

I have two DTC codes associated with this vehicle, the first you've
already addressed, and the second one is P01300. Do you know what's the
meaning of the latter?

cea1